Heretofore, drive power transmitting mechanisms for automobiles have employed a constant velocity universal joint for connecting one transmission shaft to another transmission shaft, in order to transmit rotational power to the axles.
A conventional tripod constant velocity universal joint of the above type basically comprises a tripod including three leg shafts angularly spaced 120 degrees along a circumferential direction and projecting radially outwardly, and cylindrical outer races holding the three leg shafts of the tripod so as to engage within track grooves for rotation in unison with the leg shafts. The tripod constant velocity universal joint is capable of transmitting a rotational torque at a constant-velocity regardless of the operating angle between the two shafts, while allowing the shafts to be relatively displaced in axial directions. Spherical rollers are rotatably mounted on the leg shafts in order to reduce frictional resistance between the leg shafts and the track grooves.
When the conventional tripod constant velocity universal joint transmits a rotational torque through an operating angle formed between the two shafts, the rotational torque is transmitted while spherical rollers on the leg shafts move reciprocally within the track grooves in axial directions of the outer race. The spherical rollers make one reciprocating motion per each revolution (360 degrees) of the outer races and the tripod. During such reciprocating motion, the angle of intersection between the axis of the spherical rollers and the axis of the outer races changes continuously, and the spherical rollers obliquely contact the track grooves. Therefore, the spherical rollers fail to roll smoothly with respect to the track grooves, but tend to move reciprocally while slipping against the track grooves. As a result, frictional force between the contacting members increases.
Stated otherwise, since the three leg shafts of the tripod repeat the same reciprocating motion during each rotational angle of 120 degrees, periodically induced thrust forces are produced in the axial directions of the outer races and the tripod. Such thrust forces resonate with the mount means of the engine, as well as with the transmission or the differential, tending to cause vibrations in the vehicle.
In order to reduce such induced thrust forces, Japanese Laid-Open Patent Publication No. 7-103250 discloses a constant velocity universal joint, wherein each leg shaft is inclined at a first tilt angle with respect to a plane perpendicular to the axis of the tripod. In addition, guide grooves for the outer races are defined at certain angles with respect to the tilted leg shafts, wherein the guide grooves have respective central axes inclined at a second tilt angle with respect to the axis of the tripod.
Japanese Laid-Open Patent Publication No. 11-508673 (PCT Application) discloses a constant velocity universal joint including a joint member, which has three arms (leg shafts) on which rollers are rotatably supported, the three arms being inclined a predetermined angle with respect to a plane perpendicular to the rotational axis of the joint member and the shaft elements.
Japanese Laid-Open Patent Publication No. 7-91457 discloses a constant velocity universal joint including three trunnion journals (leg shafts) having axes angularly spaced 120 degrees along a circumferential direction around the axis of a transmitting shaft, wherein the axes of the trunnion journals are not perpendicular to the axis of the transmitting shaft, but are inclined a predetermined angle with respect thereto.
Japanese Laid-Open Patent Publication No. 61-266830 discloses a constant velocity universal joint, wherein three leg shafts of a tripod are inclined at a given tilt angle with respect to a line perpendicular to the axis of the tripod, on a plane including the axis of the tripod.
Japanese Laid-Open Utility Model Publication No. 63-115927 discloses a constant velocity universal joint, wherein the axes of leg shafts are inclined at a predetermined angle with respect to a vertical plane that extends across the axis of a tripod.